08/15/2007 at 07:00 AM EDT
She's been open about wanting children – even going so far as to joke recently that she wants 15
of them – but for now, Katharine McPhee
is satisfied to just fake it.
"I [do] definitely want to have a baby, and it's fun to just pretend and look in the mirror," McPhee, 23, told Entertainment Tonight
this week about wearing a faux bump to shoot House Bunny
. "I think it'll probably hold me off a bit on having a baby.
"Today is the first day I'm wearing the prosthetic belly, which wraps all the way around [to] my back, and it's actually really comfortable," she said.
The American Idol runner-up, who told PEOPLE that she's wearing Nicole Kidman
bump to film the Adam Sandler comedy, added: "I'm really enjoying it. It's hot and sweaty though, but it's like Method acting."
The fake bump is certainly on the larger side, McPhee explained to PEOPLE, "[In this project], I'm in my ninth month, so I should be hanging kind of low."
Meanwhile, her costar in the film, Rumer Willis, is having her own troubles with cumbersome costumes. A picture of the actress featuring her character wearing just a dunce cap and silver back brace was leaked
"I keep bumping into people and having to apologize to everyone," Willis, 18, told ET
. "It's fun though ... I'm just really grateful for the opportunity."